Method of forming protective coatings on metallic sheets



Patented Mar. 21, 1939 METHOD OF FORMING PROTECTIVE COAT- INGS NMETALLIC SHEETS Henry L. Kohler, Kansas City, Mo., assignor to Andrew A.Kramer, Kansas City, M0.

N0 Drawing. Application May 21, 1937, Serial No. 144,029

Claims.

, ricated, the bending of a sheet to form a flange.

or a seam, would damage the galvanized coating on the sheet so seriouslythat it would render the coating partially ineffective, where the bendsrequired to form the flanges, or seams, were made. Consequently theadvantage of the heavy galvanized coating on the sheet was largelyiost.This was true because that portion of the sheet at which the galvanizedcoating was caused to be damaged, or ruptured, by the bending, wouldhardly be any better than an uncoated sheet, as far as resistance tooxidation, or other corrosion, was concerned, although the remainder ofthe sheet might be well coated, and would not in any manner corrodeunder ordinary circumstances. Attempts have been made to overcome thisdifficulty by a hot dipping process after fab- 0 rication, but thisentails many difficulties and requires very expensive equipment and issubstantially impossible to successfully perform,

where large sheet metal sections, such as tank sections, have beenfabricated, and are to-be 5 protected from oxidation, and othercorrosion, by such hot dipping. It is the principal purpose of myinvention to provide means for protecting a sheet that has beenfabricated, at the bend, or bends, therein, so as to prevent anycorrosion thereof at said bend, or bends, even though the originalgalvanizing coating may have been ruptured in making the bend, and toprovide a protective coating at said bend, or bends, that will be evenmore resistant to corrosion due to certain causes, than the galvanizedsheet was before bending or fabrication thereof, and which will resistevery kind of corrosion equally as well as the galvanized sheet with aheavy galvanizing coating thereon prior to its fabrication. My improvedmethod may be utilized to give a better protective coating againstcertain types of corrosion, or corrosion due to certain causes, over theentire area of the fabricated section, if

this should be desired, but is particularly in- I 5 tended for use atand adjacent the bends in the fabricated sheet, whereby any rupture inthe galvanizing coating that may have occurred during fabrication, willbe closed and the sheet protected at such bends, even more effectivelythan was the case before bending, even though a rup- 5 ture had occurredin the galvanizing coating during bending. I

In galvanizing iron, or steel, the zinc forms a thin layer of ferrouszinc alloy immediately adjacent the steel or iron of the sheet, whichhas 10 a much higher melting point than the spelter, or zinc, andimmediately sets and thus prevents any further alloying action betweenthe zinc and iron of the steel. The remainder of the spelter forms acoating of almost pure zinc overlying the coatl5 ing of ferrous zincalloy on the sheet. This outer coating of zinc varies in thickness.considerably, depending on how it is applied to the sheet. Sheets areprovided with a heavy coating of galvanizing by repeatedly dipping, orrunning the 20 sheets through the galvanizing bath. This zinc coatingdoes not have the tensile strength of steel, nor the flexibility ofsteel, and consecoated at that point. My invention entirely overcomesthisdifflculty and makes the bend, even 35 though a rupture had occurredin the galvanizing coating in the fabrication of the sheet, moreresistant to corrosion than was the case prior to fabrication, andparticularly resistant to corrosion due to sulphur compounds present incer- 40 tain oils and similar materials that may be confined in tanksthat are manufactured out of galvanized sheets with heavy coatings, suchas above referred to.

This is, accomplished by the utilization of mercury in making aprotective coating at the bend in the sheet at which a rupture of thegalvanizing coating may have occurred. Mercury may be regarded assemi-noble metal, and is particularly resistant to corrosion, because itis not 50 soluble in dilute sulphuric acid, hydrogen sulphide does notaffect it as readily as it does zinc, and the amalgams of mercury takeon the characteristics of mercury to the extent that these are alsohighly resistant to corrosion, particularly vanized sheet, particularlyat a ruptured placein said coating, by applying mercury thereto, 50

as to amalgamate the mercury with the ruptured zinc particles, some ofwhich may have detached themselves wholly or partially from theremainder of the coating. The mercury may be applied r in the metallicform, but inasmuch as some difliculty is encountered in preventing 10sof mercury because of its extremely mobile character,

it is preferred that an amalgam be made of mercury with zinc, tin,bismuth, lead, or any metal that freely dissolves in mercury, which isapplied to the part to be protected. Preferably, an amalgam of theconsistency of putty is rubbed on the metal at the place where the sameis to be protected, such as at a ruptured place in the coating on thesheet, which permits the excess to be removed with a cloth and thussaved for future use. Also the galvanizing can be amalgamated withmercury by using salts of mercury, the mercury separating out andamalgamating with the zinc It is a purpose of my invention to provide anew and improved method of protecting galvanized sheets in the mannerset forth above, and to provide a new and improved protective coatingfor sheets, and a sheet provided with such a pro- I desire to have itunderstood, however, that I do tective coating, either over the entiresurface thereof or at a bend at which a rupture in the coating may haveoccurred, or'is likely to occur. It is, of course, necessary to removethe zinc oxide, and other material, that might interfere with theamalgamating action, from the zinc at'the points at which the mercury,or mercury amal- Sam, is to be applied, by using a suitable cleaningsolution, which is applied to the galvanized coating and the excess ofcleaning fluid'removed before the mercury, or amalgam, is applied.

Other objects and advantages of my inventionwill appear as thedescription thereof proceeds.

not intend to limit myself -to the particular details described, exceptas defined in the claims.

In carrying out my improved method to produce the sheets with my new andimproved coating thereon, I first fabricate-the sheets to the desiredsize and shape and then clean each fabricated sheet at the places atwhich the protective coating is to be provided thereon. The usual methodis to clean the fabricated galvanized sheets on the outer sides of allbends therein, and in areas adjacent said bends, so that a zone not onlyat the place at which the rupture in the zinc coating may exist will becleaned, but a zone on each side thereof. The cleaning of the galvanizedsheet may chloric acid, .or with a solution of tin chloride, antimonychloride, lead chloride, zinc chloride or cyanide of soda. This cleaningsolution may be applied with a brush, or swab of some character,

' and the excessmay be removed with a cloth, or

any other suitable means. The mercury is then applied to the cleanedzone at the ruptured place in the coating and adiacentthereto, and incase metallic mercury-is used, great care should be utilized to use'onlya small amount of the metal and to spread it by brushing, or otherwise,over a large area of the clean surface of the sheet, so as to preventany material loss of mercury due be done with dilute hydroto its rollingoi! the sheet because of its great mobility,

The mercury, in being brushed over the sheet, particularly at theruptured place, or zone, in the zinc coating will amalgamate with thezinc, forming a thin coating of mercury-zinc amalgam over the entiresurface that has been cleaned, with which the mercury comes in contact.At the rupture it will combine with the zinc that is broken away fromthe sheet, forming an amalgam therewith, which will adhere to the sheetclosely and make a smooth coating, entirely closing up the break, orrupture, in the galvanizedcoating. The

amalgam thus formed will be somewhat moist at first and can be rubbedoff on the fingers to a certain extent, but will gradually harden, andafter several days, the sheet at the bend at which the mercury isapplied, will have substantially the same appearance as the remainder ofthe sheet and the amalgam will not rub off, even though the coating maybe rubbed persistently for a considerable period of time. The coatingthus formed will not be soluble in dilute sulphuric acid, nor in anyother dilute acids, being only soluble in hot, concentrated sulphuricacid.

As dilute sulphuric acid is ordinarily formed in oil tanks in which oilsare stored that have a large sulphur content, my invention isparticularly valuable for use in oil tanks that are made for the storageof such oils, which are commonly known as sour" oils. Also many 0115give off hydrogen sulphide, and ma moist atmosphere the sulphides of themetals are formed by the action of hydrogen sulphide on the metals. Thusthe zinc coating on a sheet in an atmosphere in which hydrogen sulphideand moisture is present, as will be the case in many tanks, particularlyoil tanks, will be subjected to the combined action of the hydrogensulphide and moisture, and transformed into a sulphide of zinc, which isreadily soluble in dilute sulphuric aci Where the zinc coating isruptured, iron will exposed and a sulphide of iron will be formed inasimilar manner, by the action of hydrogen sulphide and moist air. On theother hand, sulphides of mercury, lead, tin and bismuth do notdissolvein dilute sulphuric acid. Also zinc and iron sul phides oxidizerapidly in moist air to form sul- 'use of. fabricated galvanized sheetsin commercial uses, such as the making of tanks, as, not only will thezinc coating be made more protective by the amalgamation with mercury,but the ruptured portion will be made more resistant to corrosion thanwas the case prior to bending of the sheet, when the zinc galvanizingcoating was undamaged. As a matter of fact, tests made on galvanizedsheets provided with my improved protective coating, utilizing theamalgamation of mercury with the zinc to produce the same, show that theportion of' the sheet that is not ruptured and that has not beentreated, but which has the full thickness of galvanizing coatingthereon, will be attacked by dilute sulphuric acid and other means,causing corrosion, whereas, the amalgam coated portion of the sheet willnotin any manner be afiected by such corroding agents as wouldordinarily occur in practice.

Instead .of using metallic mercury, my method can be practiced withmercury amalgams. In proceeding with the method when a mercury amalgamis used, the cleaning step is carried out just as previouslydescribed,and after the cleaning of the area that is to be provided with theamalgam coating is completed, the mercury in the-form of an amalgam, isapplied. Preferably, the amalgam is made of the consistency of putty, sothat it can be rubbed on the metal with substantially no loss ofmercury. When this is done, the excess can be removed with a cloth andsaved for application to another sheet, or another'portion of the sheet.Amalgams of mercury with zinc, or with tin, or with bismuth, or withlead, or with any metal that freely dissolves in mercury, can be used tomake this puttyor paste-like amalgam. The result of the application ofsuch anamalgam to the sheet at the clean place at or adjacent therupture, or on any portion of a sheet that has been cleaned, where suchcoating is desired, results in the formingof an amalgam of the mercuryand the two metals that are present, in case the amalgam is one ofanother metal than zinc. Thus a zinc-tin-mercury amalgam, or azinc-bismuth-mercury amalgam, or a zinc-lead-mercury amalgam, can beformed on a sheet at the place that is being rubbed with the amalgam,depending on the composition of the paste-like, or putty-like, amalgam,that is rubbed on the sheet. If a mercury-zinc amalgam is rubbed on thesheet, the resulting amalgam will, of course, be a zinc-mercury amalgam.It is immaterial whether the amalgam coating is the same compositionthroughout. Thus, in applying a tin-mercury amalgam to a sheet at theruptured and adjacent the ruptured places therein, some of the mercuryin the tinmercury amalgam, will amalgamate with the zinc, forming atin-zinc-mercury amalgam, while some of the tin-mercury amalgam will bepresent without any zinc in it, and this will usually be the top surfacepart of the coating thus provided, providing the tin-mercury amalgam atthe exposed surface of the coating. A similar result would occur withamalgams of mercury and bismuth, or mercury and lead.

Instead of using either the metallic mercury or an amalgam of mercury,the zinc coating can be amalgamated with mercury by utilizing salts ofmercury, such as bichloride of mercury, the acetate or the nitrate. Inthe use of these salts the mercury will separate out as a metal andamalgamate with the zinc. A corresponding amount of zinc will bedissolved, going into combination with the acid radical of the salt, andthus be lost in the process, if any of the salts of mercury, referred'to above, are used. It is, of course, to be understood that thecleaning step is carried out to remove oxides, grease, or other foreignmatter, from the sheet at the place where the amalgamation is to take"place, when the salts referred to, are used, as well as when theamalgam, or the metallic mercury, is used for providing an amalgamcoating on the sheet.

It is, of course, to be understood that the entire surface of the sheetcan be provided with a coating that is very highly resistant tocorrosion, particularly due to the action of hydrogen sulphide in thepresence of moisture,'and dilute acids, such as dilute sulphuric acid,by amalgamating mercury with the zinc coating of the sheet over theentire area thereof, either on one or both sides of the sheet, as may befound desirable, this, of course, being done after fabrica- -tion, andit being, of course, understood that either the metallic mercury can beapplied, salts of mercury can be utilized, or amalgams of mercury withzinc, lead, tin, or bismuth, can be used to produce this protectivecoating, the result being that the entire sheet will be coated with azinc-mercury amalgam that may also contain other metals, which are moreresistant to corrosion by the agents referred to than the original zinccoating of the sheet.

What I claim is:

1. The method of increasing the resistance to corrosion of a fabricatedgalvanized metallic sheet comprising the application of mercury to thesheet after fabrication at ruptures in the zinc coating thereonresulting from such fabrication and spreading the resulting amalgam oversaid ruptures.

2. The method of increasing the resistance to corrosion of a fabricatedgalvanized metallic sheet comprising the rubbing of a putty-like amalgamof mercury and another metal on the sheet at ruptures in the zinccoating thereon resulting from such fabrication.

3. The method of increasing the resistance to corrosion of a fabricatedgalvanized metallic sheet comprising the cleaning of zinc oxide from thesame with a solvent at ruptures in the zinc coating of said sheetresulting from such fabrication, the application of mercury to saidcleaned sheet at said ruptures and spreading the amalgam thus formedover said ruptures.

4. The method of increasing the resistance. to corrosion of a fabricatedgalvanized metallic sheet comprising the application of a mercury saltto the sheet at ruptures in the zinc coating thereon resulting from suchfabrication after fabrication and spreading the amalgam with zinc thusformed over said ruptures.

5. The method of increasing the resistance to corrosion of a galvanizedmetallic sheet having ruptures in the zinc coating thereof produced byfabrication operations performed on said sheet after galvanizationthereof, comprising the amalgamation of mercury with the zinc coating ofsaid sheet at and adjacent said ruptures after such rupturingfabricating operations have been performed and spreading the resultingamalgam over said ruptures.

6. The method of increasing the resistance to corrosion of a metallicsheet shaped after having been galvanized, comprising cleaning zincoxide from the same by means of a solvent of zinc oxide at and adjacentruptures in the zinc coating of said sheet resulting from the shapingthereof, the amalgamation of mercury with the zinc coating at andadjacent said ruptures and spreading the resulting amalgam over thecleaned area at and adjacent said ruptures.

'7. The method of increasing the resistance to corrosion of a metallicsheet shaped after having been galvanized, comprising cleaning zincoxide from the same by means of a solvent of zinc oxide at and adjacentrupt'ures in the zinc coating of said sheet resulting from the shapingthereof, and rubbing an amalgam of mercury and a metal freelyamalgamating therewith on the cleaned area of said sheet at and adjacentsaid ruptures.

8. In the method of making a corrosion resisting galvanized metallicsheet having a bendtherein producing a rupture in the galvanized coatingthereon, the steps comprising cleaning zinc oxide from said sheet at andadjacent said bend and amalgamating mercury with the zinc coating onsaid sheet over the cleaned area thereof at and adjacent said bend andspreading the resulting amalgam over the ruptured area thereof.

9. In the method of making a corrosion resisting galvanized metallicsheet having a bend therein producing a rupture in the galvanizedcoating thereon, the steps comprising cleaning zinc oxide from saidsheet at and adjacent said bend and applying an amalgam with mercury ofa metal freely amalgamating therewith to said sheet over the cleanedarea thereof at and adamopao jacent said bend and spreading theresulting amalgam with zinc over the ruptured area thereof.

10. The method of increasing the resistance to corrosion of a galvanizedmetallic sheet having a damaged area in the zinc coating thereofproduced by fabrication operations performed on said sheet aftergalvanization thereof, comprising the amalgamation of mercury with thezinc coating of said sheet at and adjacent said damaged area after suchdamaging fabricating operations have been performed and spreading theresulting amalgam over said damaged area.

HENRY L. KOHLER.

